Marbling plays an important role in the price of beef. A large portion of this price deals with supply/demand. The above chart demonstrates that small changes in intramuscular fat can have a great impact on the price of beef subprimals.

Price/cwt for Choice steer carcasses that vary in USDA yield grade

In market animals, we require a certain quantity of subcutaneous fat (termed acceptable), but we grossly penalize that fat that is considered in excess (termed trimmable). In today’s market, we sort carcasses into groups of “Y 3’s or better,” “Y 4’s” and “Y 5’s” because the trim level we consider acceptable is 1 inch or less. As trim levels decrease over the years, the line for acceptability will likely shift to the left.

Muscling

Growth gradients for muscling:

(1) starts at extremities (forelimbs and hindlimbs)

(2) moves upward (chuck and round)

(3) progresses forward from rump and backward from withers

(4) meets at rib-loin juncture

Theories regarding muscling

(1) That long-bodied, tall stretchy animals are more muscular and/or yield higher percentages of steaks from certain areas of the carcass.

(2) That you can select for heavy muscling in the loin and/or round (or leg or ham) and select against muscling in the chuck or shoulder.

(3) That muscle is always present in constant ratio and proportion to bone.

(1) That long-bodied, tall stretchy animals are more muscular and/or yield higher percentages of steaks from certain areas of the carcass.

False!

With increased length of loin and rib sections, the flank and plate sections are longer, too. Thus, no net effect from a percentage standpoint.

(2) That you can select for heavy muscling in the loin and/or round (or leg or ham) and select against muscling in the chuck or shoulder.

False!

Muscles grow in concert. Thus, as you select for increased muscle in the round, muscles in the chuck will also increase.

“Expensive Muscle Group” makes up 56% of total muscle weight of cattle of very different shapes and appearance (Butterfield and Berg).

(3) That muscle is always present in constant ratio and proportion to bone

False!

Muscle:Bone

Thinly muscled 2.5:1

Normally muscled 3.5:1

Thickly muscled 4.5:1

Double muscled 5.5-8.5:1

Effect of cattle type on the ratio of major cuts (1/2-inch external fat trim) to bone

Steers

Heifers

English

Exotic

Holstein

<50% Bos indicus

>=50% Bos indicus

English

Exotic

<50% Bos indicus

Major cuts, %

46.32

46.73

46.00

46.90

47.14

46.19

46.64

45.70

Bone, %

15.68

16.04

19.17

16.56

15.97

14.43

14.91

14.95

MC:B

2.95

2.91

2.40

2.83

2.95

3.20

3.13

3.06

Source: Knapp et al., J. Anim. Sci. 67:2294 (1989)

Cattle do vary in muscle to bone and thus you cannot predict muscle:bone.

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